1. Field of the Invention
The present invention relates to a method of manufacturing a vitreous silica crucible.
2. Description of the Related Art
Single crystal silicon is usually manufactured by the Czochralski method (the CZ method). According to this method, a seed crystal is dipped into silicon melt in a vitreous silica crucible, and the seed crystal is gradually pulled up to manufacture single crystal silicon. For this method, a high-purity vitreous silica crucible is used to keep silicon melted.
The vitreous silica crucible used for pulling single crystal silicon is primarily manufactured by use of the fusing method by arc heating. In this method, silica raw material powder is supplied onto the inner surface of a rotating mold made of carbon, and the silica raw material powder is fused by arc heating by electrodes provided above the inner surface side of the mold, to manufacture a vitreous silica crucible. This way, there is obtained a vitreous silica crucible having a transparent layer hardly containing bubbles on the inner surface side of the vitreous silica crucible. However, because some bubbles remain on the surface of the transparent layer, when the transparent layer is corroded from the surface by silicon melt, the bubbles can expand or be cleaved to expose the transparent layer to the interface with silicon melt. As a result, during pulling of a silicon single crystal, the single crystallization becomes unstable, and the single crystallization yield can drop.
As the countermeasure, for example, JP-A-h01-160836 discloses a method of manufacturing a vitreous silica crucible by fusing silica raw material powder by arc fusing while depressurizing a silica powder molded body by suctioning the silica powder molded body from the mold side. In the vitreous silica crucible made by this method, the bubble content ratio in the transparent layer is drastically decreased, and thickness of the transparent layer can be thickened.
Furthermore, JP-A-2001-002430 discloses a method of supplying silica raw material powder onto the inside of a rotating mold to form a crucible-shaped molded body followed by arc heating to obtain a vitreous silica crucible, and thereafter grinding the entire inner surface of the vitreous silica crucible, and then arc heating the entire inner surface after the grinding, to completely remove bubbles in the surface of a transparent layer of the vitreous silica crucible. Furthermore, JP-A-2001-328831 discloses a method of polishing the entire inner surface of a vitreous silica crucible, and heat treating the polished surface by use of an oxyhydrogen burner, to completely remove bubbles in the surface of the vitreous silica crucible.